Extraction Science

#### **Chapter 2**

## Pyrometallurgical Approach in the Recovery of Niobium and Tantalum

*Nnaemeka Stanislaus Nzeh, Maite Mokgalaka, Nthabiseng Maila, Patricia Popoola, Daniel Okanigbe, Abraham Adeleke and Samson Adeosun*

#### **Abstract**

The pyrometallurgical methods of the recovery of various critical metals have been established. Certain pyrometallurgical approaches for niobium (Nb) and tantalum (Ta) extraction have been studied and investigated by several researchers. For instance, the conventional reduction of Nb mineral or Nb2O5 to Nb metal has been conducted over the decades. Albeit, the success level of this process, it however involves the consumption of lots of energy, high cost of equipment/equipment maintenance, somewhat low Nb and Ta recovery and limited effectiveness on low grade minerals; and thus, considered cost intensive and inefficient. In addition, the inadequacies of pyrometallurgical extraction of these metals from their complex, low grade mineral ores due to its difficulty and large energy requirement in melting the elemental impurities and gangue minerals have been a major concern. On this premise therefore, the study will provide insights into recent pyrometallurgical techniques of Nb and Ta extraction as well as associated factors and challenges.

**Keywords:** niobium, tantalum, mineral ore, reduction, roasting, fusion, precipitation, high temperature, pyrometallurgical, extraction, decomposition, beneficiation, separation, recovery

#### **1. Introduction**

The extraction and purification of metals from their mineral complex or concentrates, based on physicochemical changes occurring at elevated/somewhat high temperatures, is referred to as pyrometallurgy. Pyrometallurgical processes essentially involves certain heating procedures; usually employing dry methods conducted at high or elevated temperatures and may also involve the melting of the charge or feed material as well as high-temperature processes in which chemical reactions occur between gases, solids, and molten materials. Mineral solids composed of valuable metals are processed to make intermediate compounds for further processing or to their elemental or metallic state. Calcining, roasting and smelting operations are typical pyro-metallurgical processes that involve gases and solids, and may also result in molten products. The exothermic character of the chemical reactions occurring may be the source of the energy needed to sustain the high temperature pyro-metallurgical processes. Most frequently, fuel is being used to contribute energy to the process, or in the case of some smelting procedures, electrical energy is being applied directly. Roasting on the other hand may however involve thermal gas–solid processes, such as oxidation, reduction, chlorination, sulphation, and pyro-hydrolysis [1]. The pyrometallurgical methods of the recovery of various critical metals have been established over the decades. Certain pyrometallurgical approaches for niobium (Nb) and tantalum (Ta) extraction have been studied and investigated by several researchers in various parts of the world. For instance, the conventional reduction practice of Nb/ Ta minerals or Nb2O5/Ta2O5 to Nb/Ta metals has been conducted for several decades. Albeit, the measure of success of this process, pyrometallurgical procedure was reported to involve high temperatures and high energy consumption, high equipment cost, use of sophisticated equipment and high cost of (equipment) maintenance, somewhat low Nb and Ta yield/recovery and limited effectiveness on low grade minerals; and therefore, the process was regarded cost intensive and inefficient. In addition, the inadequacies of pyrometallurgical extraction of these metals from their complex low grade mineral ores due to its difficulty and large energy requirement in melting the value metals as well as various elemental impurities/gangue minerals have shown great concerns [2]. Despite, the large energy requirement in melting the elemental impurities/gangue minerals as a result of the complexity and low-grade nature of the minerals, successful high temperature processes/applications have been recorded, to adequately/efficiently extract and recover Nb and Ta metals from their minerals. Therefore, on this premise, the study provides insights into recent pyrometallurgical techniques of the extraction and recovery of Nb and Ta, as well as certain associated influencing factors. Thus, this chapter is concisely based on the recent pyrometallurgical approaches relating to the beneficiation, Nb and Ta extraction and recovery from mineral complexes.

#### **1.1 Niobium and tantalum chemistry**

Niobium and tantalum were discovered by British scientist, Charles Hatchett in 1801; and Swedish scientist, Anders Ekeberg in 1802, respectively. Niobium (Nb, Z = 41) has very similar geochemical properties, electronic structures and behavior (small radius/atomic size and high charge) with tantalum (Ta, Z = 73) [3, 4] and as such the two metallic elements are regarded as geochemical twins [5–7], and hence similar beneficiation and extraction techniques are usually adopted and employed for both metal elements. Nb and Ta metals are both refractory, transition, weakly acidic, BCC solid metallic elements. A lot of research work and investigations have been reported on the extraction and recovery of Nb and Ta as well as the chemistry involved in extracting both metals. From studies conducted, the Nb and Ta chemistry, hydrolysis, solubility and complexes in aqueous media have been established by various researchers [2, 8–16]. From the reports by certain researchers, it can simply be established that oxygen (O2 − ) ions have often shown very close similarities in ionic radii compared to that of fluorine (F<sup>−</sup> ) ions. Thus, there can be somewhat easy/simple substitutions occurring between O2 − and F<sup>−</sup> anions in a matrix or complexing compounds [2, 11]. In addition therefore, the hydroxides (OH<sup>−</sup> ) also possess somewhat similar chemical characteristics/properties as well as in geometry with F<sup>−</sup> anions. This similarity is especially and essentially found in their charge and size; and thus, a justification (scientifically), of somewhat easy and feasible substitutions that may occur between their complexes/compounds in the chemical and/or thermodynamic reactions. Therefore, apart from O2−, Ta and Nb are hypothesized also, to be very

#### *Pyrometallurgical Approach in the Recovery of Niobium and Tantalum DOI: http://dx.doi.org/10.5772/intechopen.109025*

liable of forming or producing soluble complexes or compounds with certain strong ligands, such as: OH<sup>−</sup> and F<sup>−</sup> [2, 17, 18]. More so, Nb and Ta are particularly somewhat soluble (in wt. % levels) with alkaline melts or solutions [2, 18, 19], and might even as well attain greater solubility with carbonatite molten solutions [2, 18, 20]. **Figures 1** and **2** depicts the basic description and representation of Nb and Ta metals, respectively, indicating that they are refractory, transition, weakly acidic, BCC solid metallic elements.

#### **1.2 Niobium and tantalum minerals**

Nb and Ta primary mineral ores are natural occurring complex oxide minerals, mostly of low grade deposits with chemical composition majorly composed of different content levels of Nb and Ta refractory metals' penta-oxides (Nb2O5 and Ta2O5), iron (Fe2O3), manganese (MnO), tin (SnO2) and titanium (TiO2) oxides with other refractory, metallic oxides. Nb/Ta minerals occurring as penta-oxides (Nb2O5/ Ta2O5) are often associated together in similar mineral structures. Over the years, a lot of researchers have consistently and extensively studied the recovery and extraction of Ta and Nb from their primary deposits or mineral ores as well as their secondary sources, applying various mineral processing steps and certain beneficiation/separation methods. More recently, Nb and Ta have been extracted from several primary rock deposits and mineral ores. Howbeit, these primary deposits/mineral ores of

#### **Figure 1.** *(a) Nb element; (b) samples of Nb metal [21–23].*

#### **Figure 2.**

*(a) Ta element; (b) samples of Ta metal [21, 23].*



*Major Nb and Ta mineral resources [2, 11, 23, 25, 26].*

Ta and Nb are somewhat scarce in the world and are naturally deposited with a low average crustal abundance of about 2 and 20 mg/kg, respectively. Hence, this in their classification, are referred to as rare metals [15, 16, 23, 24]. **Table 1** displays important Nb-Ta minerals along with their major characters.

#### **1.3 Niobium and tantalum extraction**

The demand of Nb and Ta has consistently become somewhat higher than the supply. However, the extraction and recovery of Nb and Ta from their minerals and from other elements contained in the mineral composition, has become very tedious and difficult, involving very complex processes and techniques. Also, the choice selection and application variation of the mineral enrichment, beneficiation and extraction techniques has become somewhat tedious and complicated as they practically depend on the mineralogy of the mineral ore or concentrate, its nature and type, level of purity and impurity, number of safe beneficiation/extraction process steps and most importantly, on the physicochemical properties of the mineral with respect to the chemical composition (the physical and chemical nature/properties of the value and gangue minerals [2, 23]. **Table 2** depicts certain major determinant or influencing factors to be considered when selecting suitable techniques for extraction/recovery of Nb/Ta.

The extraction efficiency of Nb and Ta from mineral deposits greatly depends on the measure or degree of removal of associated impurities present in the crude Nb mineral ore [28]. Hence, for a successful Nb and Ta metal extraction (for both pyrometallurgical and pyro-hydrometallurgical procedures), the impurity content in the oxide mineral ore and the choice of beneficiation/extraction methods and/or extraction agents are key [29]. Thus, a successful beneficiation/separation process application is often rated on the basis of the obtained percentage recovery of the high-purity valuable minerals as well as the impurity content being reduced to a minimum with fewer processing/recovery steps [2, 16]. In addition, low-grade Nb/Ta minerals mined mechanically, such as columbites and tantalites have been reported to contain a lot of impurities and sometimes have less than 0.1% Nb2O5/Ta2O5 contained in the mineral ore. This increases the difficulty in the mineral processing and subsequent metal recovery. Thus, an efficient ore enrichment beneficiation process route is important to effectively improve the metal extraction and significantly eases up the subsequent downstream pyro- or hydro-metallurgical decomposition and separation processes of the mineral for successful Nb and Ta recoveries. Hence, the need for the minerals to undergo beneficiation/enrichment processes for ore upgrade to an industrially acceptable metallurgical grade of minimum composition of 25% Nb2O5 and Ta2O5 or 50% in their combine form, which is the required content in the ore for effectiveness/ efficiency of subsequent downstream extraction process [30].

Howbeit, due to the complexity and presence of impurities such as: refractory/ metallic oxides, rare earths and radioactive elements; Nb2O5 and Ta2O5 are usually hydrometallurgically extracted from its mineral ore source using hydrofluoric (HF) acid as the decomposition agent before separation and recovery. The traditional method of extraction of Nb and Ta from primary mineral resources using hydrometallurgical procedures namely; employing aqueous dissolution and subsequent solvent extraction (SX), ionic exchange (IX) or other separation/purification processes [31, 32] is well documented in literature. However, some of these process steps are usually employed under harsh aqueous media conditions of very toxic, concentrated, hazardous and corrosive chemicals with several complex separation steps [33].


#### **Table 2.**

*Factors considered when selecting Nb and Ta extraction/recovery process routes [16, 23, 27].*

This is chiefly due to the insolubility rate of Nb, Ta and other refractory metallic oxides in milder conditions [32, 34]. The chemical and physical similarities of Ta and Nb with other refractory elements make their separation from mineral ores a complex and difficult process [35]. Over the decades, several pyro- and hydro-metallurgical processes of the extraction/recovery of Nb and Ta have been established by various researchers. For instance, Jean Charles Galissard de Marignac developed a hydrometallurgical process in 1866, popularly referred to as the "Marignac process" for Nb and Ta extraction. This very method involved fractional crystallization process in order to separate the metals as potassium oxypentafluoroniobate monohydrate (K2[NbOF5] H2O) and potassium heptafluorotantalate (K2[TaF7]), respectively. This in turn was also reduced in order to obtain the metals of certain high purity [2, 36], most times adopting the process of electro-winning in fused salts [2, 13]. Howbeit, the establishment of liquid–liquid extraction (LLE) in the 20th century replaced the Marignac method. This process was however developed by the Ames Laboratory and the U.S. Bureau of Mines in 1957. The method utilized the difference in acid solubility of Nb and Ta F− ions in organic solvents at specific acid levels [2, 10, 37–40].

In recent times, several researchers and investigators enhanced this Nb/Ta extraction method and also, various novel process applications have been studied and developed. The digestion of Ta and Nb mineral particles and subsequent stepwise/ selective separation of the metals from their reaction complexes; however considering the recovery and purity level, cost and economic aspects, energy and reagent consumption [2, 41], waste and environment management issues. Among methods adopted by these researchers in order to achieve simultaneous digestion and decomposition of Ta and Nb minerals were chlorination process, alkali fusion method, alkali fusion-acid leaching, alkaline solution dissolution, ammonium fluoride (NH4F) and ammonium bifluoride (NH4HF2) fusion, decomposition with direct H2SO4 acid or combined with HF acid, [2, 9, 42–45]. Howbeit, the most successful method employs the initial halogenation and dissolution in HF acid or a combination of HF acid or a fluoride medium like fluoride salts (which forms oxy-fluorides) with mineral acids

#### *Pyrometallurgical Approach in the Recovery of Niobium and Tantalum DOI: http://dx.doi.org/10.5772/intechopen.109025*

[2, 26, 39, 40, 43, 45–48]. This is usually achieved at somewhat high temperatures and concentrations, and under harsh, hazardous and corrosive operational conditions [9, 26, 43, 49, 50] due to the resistance of Nb-Ta mineral ores to chemical/acid attack at mild conditions [32, 39, 40, 48, 51, 52]. Hence, with selective leachants like HF acid, hydrometallurgical techniques was completely adopted and recommended suitable, as a result of its lesser consumption of energy and higher recovery/grade purity of Nb products essentially from complex and low grade mineral ores [52, 53]. However, with stringent regulations on health, safety and environment (HSE) increasing significantly every day, adoption of this hydrometallurgical process has since then, suffered its own share of demerits due to toxicity and harmful nature of HF and other fluoride media [44, 52, 54, 55].

Howbeit, the present limitations involved in the conventional use of HF acid for leaching and dissolution of Nb and Ta minerals ranges from the loss of HF acid through volatilization during the metals' extraction, of about 6–10% Vol. (pressure of 763 mm Hg at room temp), the great amounts of HF acid wastes generated that contains fluoride salts and the serious challenge it poses to personnel and the environment with respect to waste management as well as the safe disposal of such waste fluoride salts. Thus, it can be related that the high corrosiveness, toxicity, volatility, chemical consumption and cost, generation of fluoride-bearing waste water, and other environmental related issues of HF acid, thus contribute to the difficulty and complexity of the extraction/separation process route, as well as the high equipment maintenance/operation cost. Due to these shortcomings as well as the low recovery yield of Ta and Nb, the demand for these metals is somewhat higher than their supply. This is as a result of their criticality and numerous engineering/technological applications, such as: the utilization in the production of rocket missiles, aircraft engines, telephones, solar cells, turbine blades, capacitors, HSLA/stainless steels, oil/gas pipelines, particle accelerators, nuclear reactors, super conductors, refractive index of lenses, heat resistant/ cutting tools [2, 23, 56]. Thus, a great deal of research investigation is imperative for enhancing or developing simpler, cleaner, effective and less complicated Ta and Nb extraction/separation process route in order to obtain optimum recoveries and resource utilization. On this premise therefore, several researchers have established the need to develop fluoride-free mineral decomposition media under mild conditions as substitute or alternative extraction procedure for Nb and Ta recovery. Albeit several investigations conducted on Nb and Ta extraction process route from their various mineral resources, research is still on-going in order to completely establish and develop a more efficient process alternative or substitute route for the dissolution/decomposition of the minerals; with very significant efforts ascribed towards mitigating the draw-backs and shortcomings of the conventional extraction/separation of Nb and Ta adopting HF acid as the dissolution medium. As a result of the various challenges encountered in the separation of Ta and Nb from associated impurities in their minerals and from each other, it thus became necessarily important to explore/exploit several extraction and recovery processes. Therefore, it is only imperative that serious attention should also be attributed to the pyrometallurgical as well as the pyro-hydrometallurgical approaches for optimum/efficient Nb and Ta extraction/recovery from their minerals.

#### **2. Pyrometallurgical approaches**

Over the years, the pyrometallurgical approach of Nb and Ta extraction has been established. Several authors have reported their investigations on the conventional

pyrometallurgical reduction of Nb/Ta penta-oxide to the metal [36]. However, this process often consumed a lot of energy, high reagent consumption, high cost of equipment/equipment maintenance, low Nb/Ta recovery and limited effectiveness on the Nb/Ta low grade minerals; and thus, certain researchers considered the process application inefficient and not cost effective [52]. Habashi [53] reported the inadequacies of the pyrometallurgical extraction of the metals from their complex and low grade minerals due to the extraction difficulty, high temperature and large energy requirement in melting the elemental constituents and gangue minerals. Hence, with selective leachants like hydrofluoric (HF) acid, hydrometallurgical techniques have been completely adopted and recommended suitable, as a result of its lesser consumption of energy and higher recovery/grade purity of Nb products essentially from complex low grade minerals [52, 53]. However, with stringent regulations on health, safety and environment (HSE) protection increasing significantly every day, the adoption of this hydrometallurgical process has since then, suffered its own share of demerits due to the high eco-unfriendliness, toxic and harmful nature of the adopted HF acid and other fluoride extraction media [44, 52, 54, 55], in comparison to the pyrometallurgical techniques. Recently, a lot of research works have been directed towards the pyrometallurgical extraction of Nb and Ta, especially as an adjunct process for optimum and efficient recovery of the metals. More so, despite the inadequacies and shortcomings involved in pyrometallurgical techniques, more especially the employment of elevated temperatures, certain positive effects however can be achieved during high temperature extractive procedures on complex minerals. Thus the following establishments:


#### **2.1 Pyrometallurgy and high temperature extraction techniques**

Pyrometallurgical procedures on the treatment of Nb and Ta minerals or complexes may involve certain thermal and chemical processes and reactions which may lead to the modification and formation of entirely new mineral phases.

*Pyrometallurgical Approach in the Recovery of Niobium and Tantalum DOI: http://dx.doi.org/10.5772/intechopen.109025*

#### *2.1.1 Roasting process*

Roasting as a pyrometallurgical procedure involves gas–solid reactions at elevated temperatures with the aim of mineral/metal decomposition, separation and purification. Roasting of mineral complexes or concentrates is often regarded a thermo-chemical process where the chemical conversion of the mineral takes place with oxygen or some other elements or compounds employed at somewhat high temperatures, converting it into another chemical form or state. This is a route or step that has been adopted by several researchers in the processing of certain Nb and Ta complexes or mineral concentrates, usually conducted in order to prepare the mineral for an adjunct hydrometallurgical procedure. For instance, the feasibility of leaching or dissolution process is at an increased measure if the metals in question are in their less stable (oxide) forms and thus more soluble and easy to dissolute. This is usually the situation after the mineral complex has undergone roasting procedure, either on the Nb and Ta complexes or on other mineral impurities/gangue associated in the mineral matrix. Howbeit, before roasting is performed, the minerals often times undergo some physicochemical beneficiation and separation process to some extent, such as froth flotation, gravity, magnetic or electrostatic concentrations. The mineral concentrate may be mixed with certain reagents or materials in order to aid/ enhance roasting. Mineral oxides can be somewhat easily reduced to their metallic state or elemental form compared to sulphide minerals. Typically, the roasting of Nb and Ta mineral complexes may often involve certain complex thermal and chemical gas–solid reactions taking place between the mineral/material solids and the furnace atmosphere; and this however consists of several process types.

#### *2.1.2 Roasting types*

#### *2.1.2.1 Oxidative roasting*

This is the most common type of roasting process industrially practiced and it's more often employed on sulphide complexes or mineral concentrates. In this type of roasting process, the (sulphide) complex is converted to oxides and sulfur is thereby given off as sulfur dioxide gas (SO2). The complex is however heated to elevated temperatures in the presence of excess oxygen or air in order to completely or partially burn out or replace the impurity elements (which in most cases is usually sulfur) with oxygen. Here, introduced oxygen is supplied and hence replaces the sulfur being burnt off. However, this procedure is usually considered environmentally unfriendly as harmful sulfuric gases are released into the environment. Howbeit, it is essential to note that the sulfur gas released in the form of sulfur dioxide gas (SO2) may be trapped and essentially utilized in the production of sulfuric acid (H2SO4). At the occurrence of complete or almost complete sulfur removal from the sulphide complex, the residue is referred to as dead roast. In this type of roasting, quartz and certain other gangue minerals may act as catalyzers. The general oxidative roasting chemical reaction is represented in Eqs. 1 to 2.

Metal sulphide —› Metal oxide.

$$\text{MS}\_{\text{(c)}} + \text{3/2}\,\text{O}\_{\text{2(g)}} \to \text{MO}\_{\text{(c)}} + \text{SO}\_{\text{2(g)}}\tag{1}$$

$$\text{2MS}\_{\text{(s)}} + \text{2O}\_{\text{2(g)}} \to \text{2MO}\_{\text{(s)}} + \text{2SO}\_{\text{2(g)}}\tag{2}$$

#### *2.1.2.2 Chloridizing roasting*

This roasting process type involves the transformation or conversion of certain mineral complexes or metallic compounds to chloride forms either by employing reduction or oxidation processes or conditions. This type of roasting can be employed to extract and process certain metals from their chloride state or forms; such as Nb, Ta, Be, Ti, Zr, as well as U and certain rare earth elements (REE). Some overall chloridizing roasting forms is represented by the chemical reactions in Eqs. 3 and 4. The Eq. 3 represents the chlorination process of a sulphide mineral complex which involves an exothermic reaction; while Eq. 4 presents the involvement of an oxide mineral complex with the addition of elemental sulfur serving as a catalyst and facilitating the chemical reaction. More so, some carbonate mineral ores also react almost similarly as the oxide mineral ores after being decomposed or digested under certain elevated temperatures to their oxide state.

$$\text{M2NaCl} + \text{MS} + \text{2O}\_2 \rightarrow \text{Na}\_2\text{SO}\_4 + \text{MCl}\_2 \tag{3}$$

$$2\text{ 4NaCl} + 2\text{MO} + \text{S}\_2 + \text{3O}\_2 \rightarrow 2\text{Na}\_2\text{SO}\_4 + 2\text{MCl}\_2 \tag{4}$$

#### *2.1.2.3 Volatilizing roasting*

This roasting type is the volatilization or elimination of the metallic oxides such as ZnO, As2O2, Sb2O2 and some other oxides from the mineral complex. Volatilizing roasting however involve the careful oxidation of mineral ores at high temperatures in order to remove unwanted elements or impurities in their volatile oxide state or form. In this type of roasting process, the careful control of the amount of oxygen in the roaster is imperative as the excessive oxidation of the mineral complex may produce non-volatile oxide complexes.

#### *2.1.2.4 Magnetic roasting*

This type of roasting involves the controlled reduction of certain metallic mineral complexes, converting them into their metallic forms, in order to ease up subsequent beneficiation, separation and processing routes or steps. For instance, a non-magnetic iron oxide, such as hematite (Fe2O3) is reduced in a controlled reduction reaction to magnetite (Fe3O4), a more magnetic iron form or state, prior to magnetic separation and/or other concentration processes. This method of roasting has been employed for the concentration of certain Nb and Ta mineral complexes by several researchers with the aim of recovering or eliminating associated iron content.

#### *2.1.2.5 Reductive roasting*

This type of roasting process involves the partial reduction of an oxide mineral ore, in preparation to the actual smelting reduction process or hydrometallurgical extraction or recovery of the metal from the mineral ore to its metallic form or state. This is regarded as the most adopted and successful form of roasting on Nb and Ta minerals/complexes.

*Pyrometallurgical Approach in the Recovery of Niobium and Tantalum DOI: http://dx.doi.org/10.5772/intechopen.109025*

#### **2.2 Calcination process/thermal treatment**

Prior to calcination, a precipitation process is usually conducted on the Nb and Ta products/leachates obtained fromthe downstream hydrometallurgical procedures, generating certain intermediates of Nb and Ta as precipitates, and often in the form of pentaoxides or probably dry hydroxides. The structure of the washed/filtered precipitates may contain either two kinds of water. The first kind of water is incorporated within the Nb(V) and Ta(V) hydroxides, and can only be eliminated with calcination employed at somewhat higher temperatures within the range of 700 to 900°C. The other kind of water is known to be intrinsic moisture and may easily be eliminated by only employing a drying process at lower temperature range within 100 to 200°C.Calcination of the processed Nb and Ta complexes or precipitates may result in the yield of high purity Nb and Ta oxides. Calcination process however, also leads to the elimination of certain volatile constituents that were entrained in the precipitates, such as ammonium or fluoride [2, 25]. The calcination/water removal process may be simply presented as in Eqs. 5 and 6.

$$2\text{Nb(OH)}\_{\text{\textsuperscript{\text{\tiny}}}} + \text{Heat}\_{\text{(700-900}\text{O}\_{\text{C})}}\\\text{o} \rightarrow \text{Nb}\_{2}\text{O}\_{\text{\tiny g}} + \text{5H}\_{2}\text{O}\tag{5}$$

$$\text{2Ta(OH)}\_{\text{\textsuperscript{\text{\tiny{}}}}} + \text{Heat}\_{\text{(}700-900} \text{o}\_{\text{C})} \rightarrow \text{Ta}\_2 \text{O}\_{\text{\tiny{}}} + \text{5H}\_2 \text{O} \tag{6}$$

#### **2.3 Thermal production of Nb and Ta metals**

The yield or production of Nb and Ta as pure metals is essentially dependent on their forms which they were found in the metal intermediates. For instance, the Nb metal is often achieved by the reduction of its intermediates employing reducing chemical agents like Al, Ca, Mg, H, Na or any suitable electron donors. The most widely practiced/adopted approach is based on the use of Al and is referred to as aluminothermic process, consisting of reactions between the pentaoxides (Nb2O5) and the pure Al at certain temperatures >1100°C, as shown in Eq. 7. However, the Ta metal refining from potassium heptafluorotantalate is mostly obtained by its reduction with Na (in Eq. 8). It is recommended however, that in order to achieve high purity Ta metal, both the salt as well as the Na-bearing reducing agent should be of high purity. The chemical reaction is to take place at approximately 1200°C temperature inside the reactor that operates under an inert atmosphere or vacuum, in order to prevent the accumulation of oxygen during the reduction procedure. The chemical reaction that occurs is therefore exothermic and have been reported to release about an energy of about 2985 kJ/kg [25, 57].

$$\text{Nb}\_2\text{O}\_8 + \frac{\text{10}}{\text{3}}\text{Al} \rightarrow 2\text{Nb}\_{(\text{s})} + \frac{5}{\text{3}}\text{Al}\_2\text{O}\_{3(\text{s})}; \Delta\text{H} = -890 \text{kJ/mol} \tag{7}$$

$$\rm{K}\_{2}\rm{TaF}\_{7} + \rm{5Na} \rightarrow \rm{Ta} + \rm{5NaF} + \rm{2KF} \tag{8}$$

#### **2.4 Influencing factors**

The selection of appropriate existing, developing or newly developed novel beneficiation and extraction process routes, decomposition and separation techniques that are suitable for complex Ta and Nb mineral matrices and concentrates is highly dependent on specific factors. Other than the physical and chemical factors or properties, which includes: the mineral type, nature, and chemical composition, there are other factors that may affect the selectivity/choice of the process steps and dictate the process application of extraction and separation process routes, such as: the technical, environmental, economical, safety and quality factors. This may also include the ability/feasibility of obtaining high purity/high yield recoveries, with minimal consumption of energy, number of process steps, by-products and environment pollution. Cost and scalability from laboratory to industrial/commercial scales are also considered major factors [16, 23]. The cost factor however may include the price cost of the mineral type, price cost of the processed materials, fuel cost and availability as well as product quality/quantity [23, 27]. More so, certain determinant factors or parameters may influence the degree of success as well as the decomposition rate of the roasting of Nb and Ta complexes. This includes: temperature, time, physicochemical condition of the mineral complex, chemical reagent type, availability/cost of the reagents or additives, mineral sample to reagent ratio, reagent concentration, mixing ratio, stirring speed, stirring time, equipment or furnace as well as the eco-friendly/unfriendly nature of the chemical reagents employed and the reaction process.

#### **3. Literature overview of the pyro-hydrometallurgical recovery of Nb and Ta**

Various pyrometallurgical processes have been adopted by several researchers for the extraction and recovery of Nb and Ta. Howbeit, the high temperature and high thermal energy consumption has poised a major setback. Thus this very process is usually adopted with certain adjunct processes, in order to reduce the temperature applied, thermal energy consumption as well as the cost implications. Moving forward, a lot of researchers have concurred that alkali fusion, an old and earliest established industrial method for mineral decomposition [43–45], and the alkali roasting-leaching decomposition process have been employed on Nb and Ta minerals with certain degree of success. The reaction chemistry, complexes and solubility rate or efficiency of Nb and Ta in alkaline media has thus, been investigated by various researchers [18, 19, 43–45, 47, 58–66]. Alkali roasting technique as a decomposition process has also been investigated by researchers [26]. Few investigations have been reported on the efficacy of alkali reductive roasting and dissolution of Nb/Ta ore minerals or concentrates. Nevertheless, there is still need to adopt mild concentrations/consumption of the alkali reagents with reduced/moderate temperatures. Also, most successful decomposition processes were however established effective to a certain measure on high-grade minerals but not effective on low-grade minerals [2, 4]. However, alkali roast and leach dissolution method employing KOH roasting and H2O leaching on a low-grade Nb-Ta mineral ore has had great recoveries [44, 47]. KHSO4 fusion as a pyrometallurgical process to improve the subsequent leaching efficiency of a low grade Nb/Ta polymineralized ore has also been adopted [62]. The study reported the feasibility of Ta/Nb decomposition and leach recovery efficiencies of alkali dissolution process on low-grade minerals. Hence, the reductive roast mineral treatment utilizing certain alkali agents was regarded an eco-friendly process and thus, a promising extraction route with moderate leachant and energy consumptions. Howbeit, high roasting temperatures and alkali reagent consumptions were main set-backs.

#### *Pyrometallurgical Approach in the Recovery of Niobium and Tantalum DOI: http://dx.doi.org/10.5772/intechopen.109025*

For instance, Ghambi et al. [56] investigated a novel pyrometallurgical procedure for extracting and purifying columbite and tantalite concentrates (29% Ta2O5 and 16% Nb2O5). A reductive roasting procedure was employed in the study. The Nb and Ta concentrates were reduced with solid carbon in the form of activated charcoal (carbothermic reduction) and alkali as the reducing atmosphere employing high temperatures ranging from 800 to 950°C. This was reported to aid the reduction of the iron oxides present in the concentrates to metallic iron as well as the subsequent magnetic separation. Suri *et al*. [58] investigated the alkaline decompositions for recovery of Nb and Ta from a cassiterite (Sn) bearing mineral, using Na2CO3 and K2CO3 salts. The authors reported successful recoveries of Nb and Ta employing alkaline fusion/reduction roasting-acid leaching processes. Phase transformations of pellets of Sn oxides such as SnO and SnO2, and Na2CO3 alkaline salt when roasted under certain carbothermic (CO-CO2 mixed gas) thermal atmospheres were investigated by Liu *et al*. [66]. The resulting highly pure pellets of Na2SnO3 reported by the researchers confirm the favorable reaction chemistry of certain alkaline salts on the pyrochlore mineral group. Nete *et al*. [67] however explained the feasibility of adopting the alkali flux decomposition process as a substitute digestion method. Albeit the low Nb and Ta recoveries of microwave digestion, their investigations displayed process simplicity and also showed that the process allowed smaller amounts of chemical reagents for digestion. The authors also concluded that flux fusion with lithium tetraborate had shorter time for digestion and high recoveries of >90%; however larger amounts of chemical reagents and time-consuming sample preparations were needed for digestion.

As a result of the volatilization and loss of toxic/corrosive HF acid during dissolution process of Nb-Ta minerals, resulting to equipment corrosion and harm to human beings and environment, Yang *et al*. [45] established a novel process decomposition of low-grade Nb/Ta minerals. The researchers employed alkali fusion method, applying caustic soda (sodium hydroxide, NaOH) with minimum alkali consumption of alkalisample ratio reduced from 3:1 to 1:1. A reduced alkali-sample ratio of 1:1, initial mineral particle size of 75 μm and 650°C temperature for 30mins had significant influence on the Nb/Ta mineral decomposition. The mineral was however converted to Na(Nb,Ta) O3 complexing compounds and not that of Na3(Nb,Ta)O4, which is usually realized from the conventional alkali fusion method. Results however indicated mineral decomposition efficiencies of 98% cassiterotantalites and 99% pyrochlores in the Nb/ Ta ore. Howbeit, K(Nb,Ta)O3 and Na(Nb,Ta)O3 compounds/complexes are somewhat not soluble in most mild solutions. Also, Berhe *et al*. [68] carried out the comparison of the performance and decomposition of the kentichamangano-tantalite ore by both HF-H2SO4 leaching and KOH fusion-leaching. The comparative study thus proposed KOH sub-molten salt as a substitute process method for the dissolution of Nb/Ta minerals with the intention of mitigating/eliminating HF acid pollution and associated harm or hazards. Results also explained that the dissolution rate is dependent on the proportions/concentrations of the HF-H2SO4 and KOH leaching agents. In addition therefore, higher ratios of HF to H2SO4 in the acidic system and higher concentrations of KOH during the alkaline fusion process step led to lesser amounts of leftover residues after the decomposition process thereby resulting to better or increased dissolution rates after H2O leaching. Thus, the authors however concluded that KOH possess the potential of being a suitable alternative or substitute material to the conventionally utilized HF acid. Similarly, De Oliveira, De Souza and Lopes-Moriyama [69], conducted investigations on alkaline thermal treatments with subsequent acid leaching on a ferro-columbite mineral in order to obtain mixed proportions of Ta and Nb oxides. The study however reported good yield recoveries, employing alkali fusion with



*Pyrometallurgical Approach in the Recovery of Niobium and Tantalum DOI: http://dx.doi.org/10.5772/intechopen.109025*

*Key: MLA = Mineral liberation analyzer;LG = Low grade; HG = High grade; SX = Solvent extraction; IX = Ionic exchange; MIBK = Methyl isobutyl ketone; MIAK = Methyl isoamyl ketone; EMIC = 1-ethyl-3-methyl imidazolium chloride; PPDA = ρ-phenylenediamine; LPA = Laser particle analyzer; PPT = Precipitation; EDXRF = Energy dispersive X-ray fluorescence; XRPS = X-ray photoelectron spectroscopy; XRPD = X-ray power diffractometry; Concs = Concentrates; SEM = Scanning electron microscopy; EDXS = Energy dispersive X-ray spectroscopy; OPM = Optical microscopy; AAS = Atomic absorption spectrophotometry; BET = Brunauer–Emmett–Teller; ICP-OES/AES = Inductively coupled plasma-optical/atomic emission spectroscopy; FT-IR = Fourier transform-infrared spectroscopy; TGA = Thermogravimetric analysis.*

#### **Table 3.**

*Nb-Ta pyro(hydro)metallurgical extraction procedures adopted by various researchers.*

potassium bisulphate (KHSO4) and subsequent HCl acid leaching. More so, mechanical pre-mixing process has been established on primary minerals and reported to aid proper distribution of the chemical reagents on the mineral particles, thus, enhancing pyrometallurgical decomposition [70]. **Table 3** therefore summaries the major pyro(hydro)metallurgical extraction methods recently adopted by researchers.

### **4. Conclusion**

The separation and recovery of Nb/Ta metallic elements from mineral deposits has become somewhat challenging, involving several complex/complicated extraction process routes from the rest of the gangues/impurity elements composed in the mineral ore or deposit and from the value metal elements themselves. This can be chiefly attributed to the presence of numerous impurities such as: metal oxides, refractory, rare earth (REE) and radioactive elements, and hence the complexity of the metal extraction process. In that regard, Nb2O5 and Ta2O5haveconventionally been extracted hydrometallurgically, using HF acid as the dissolution agent, or a combination of HF and H2SO4 mineral acid dissolutions. Howbeit, the high volatility, corrosive and toxic nature, high chemical/reagent consumption, eco unfriendliness and waste generation of fluorides have contributed to Nb/Ta extraction complexity, high equipment maintenance and high operational cost. This, as a result has increased the extraction difficulty and low yield recovery/purity of the metals, coupled with their numerous industrial applications in engineering and technology. This study therefore has provided insights into recent adopted pyro- or pyrohydro-metallurgical Nb/Ta extraction process routes as well as its associated factors. Certain pyrometallurgical techniques, such as reductive roasting, carbothermic reductions, alkali roasting and alkali fusions, etc. have shown great success in Nb/Ta extraction. Regardless of the drawbacks encountered, such as elevated temperature and high energy/reagent consumption, the adoption of high temperature procedures is imperative as it plays key roles in the decomposition of these value metals, in preparation for subsequent downstream measures. Thus, the employment and development of pyrometallurgical extraction routes for efficient Nb/Ta recovery is therefore encouraged with certain process advances/improvements, proper process optimization, as well as adoption of adjunct techniques so as to mitigate/curtail such limitations.

### **Acknowledgements**

We sincerely acknowledge the Faculty of Engineering and the Built Environment, Tshwane University of Technology, Pretoria, South Africa. Most especially, our special recognition and hearty appreciation goes to Adeline C. Nzeh and also to Dr. Swithin N. Nzeh (G.P, United Kingdom; MBBS, MRCGP, Dip. Paed, RCPathME) for their significant contributions towards the success and actualization of the present study.

*Pyrometallurgical Approach in the Recovery of Niobium and Tantalum DOI: http://dx.doi.org/10.5772/intechopen.109025*

#### **Author details**

Nnaemeka Stanislaus Nzeh1 \*, Maite Mokgalaka1 , Nthabiseng Maila1 , Patricia Popoola1 , Daniel Okanigbe1 , Abraham Adeleke1,2 and Samson Adeosun3

1 Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria, South Africa

2 Department of Materials Science and Engineering, ObafemiAwolowo University, Ile-Ife, Nigeria

3 Department of Metallurgical and Materials Engineering, University of Lagos, Akoka, Nigeria

\*Address all correspondence to: nstannzeh@gmail.com

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 3**

## Alternative Extraction Systems for Precious Metals Recovery: Aqueous Biphasic Systems, Ionic Liquids, Deep Eutectic Solvents

*Olga Mokhodoeva*

#### **Abstract**

The current trend in the development of separation methodologies implies their evolution in an environmentally friendly perspective, more precisely, the transition to techniques, materials, and solvents that could be qualified as greener alternatives to conventional ones. The green extraction systems can be attributed to aqueous biphasic systems, ionic liquids, and deep eutectic solvents, which have been widely used recently for various analytical, synthetic, and industrial tasks. In this chapter, the features of the listed systems are discussed in relation to the extraction of precious metals, mainly platinum, palladium, and gold; the examples of the alternative extraction systems for separation and preconcentration of precious metals are reviewed.

**Keywords:** extraction, precious metals, platinum group metals, aqueous biphasic systems, ionic liquids, deep eutectic solvents, recycling, green chemistry

#### **1. Introduction**

Platinum, palladium along with their satellites (platinum group metals, PGMs), and gold are essential and often irreplaceable in many areas of science and industry, including rapidly developing fields of electronics, automobile and engineering industry, medicine, and so on. Going forward, there is a high potential for new PGMs' use in energy transition applications [1–3]. The limited natural reserves and the steadily growing demand for precious metals dictate an improvement of technologies for processing the primary raw materials and especially secondary resources, namely spent automotive catalysts and electronic wastes [4–7]. At the same time, selective recovery of precious metals is also an important analytical problem, because it represents a crucial step in their accurate determination. This problem is relevant for searching and evaluation of new deposits and study of alternative sources, as well as for obtaining data on monitoring PGMs in the environment and biological fluids [8].

Various methods for processing platinum-containing materials and recovery of precious metals based on co-precipitation [9, 10], solvent extraction [11], sorption [12], electrodeposition [13], molecular recognition [14], and so forth are explored.

The vector of progress of the mentioned methods, coinciding with that for chemical and process industries as a whole, is aimed at finding tools that align with the principles of green and white chemistry and the interests of sustainable development [15–17]. From this standpoint, utilization of alternative solvents and extraction systems of new generation is of great scientific and practical importance. As such systems, aqueous biphasic systems, supramolecular solvents, supercritical fluids, and the so-called designer compounds—ionic liquids and deep eutectic solvents—are currently considered. Some of them are addressed in this chapter relating to precious metals extraction for both technological and analytical applications.

#### **2. Aqueous biphasic systems (aqueous two-phase systems)**

Phase-forming components of aqueous biphasic systems (ABSs) are water-soluble, nontoxic, biocompatible, available, and produced in large quantities. Recently, along with traditional polymer-salt and polymer-polymer systems, ABSs produced on the basis of non-polymeric compounds, such as organic salts, in particular ionic liquids, hydrophilic solvents (acetonitrile, alcohols), and so on, have been proposed [18, 19].

Technologies for producing and purifying enzymes and other biomolecules using ABSs based on biodegradable polymers have been developed and successfully introduced into industry [20–22]. Studies on the extraction of metals, mainly nonferrous, radioactive, transplutonium, were first described in the 80s of the last century [23].

The data on extraction of precious metals in ABSs are limited to only a few publications (see **Table 1**). One of the first works by Bulgariu [24] described the extraction of gold(III) using an ABS prepared by mixing polyethylene glycol PEG-1500 and (NH4)2SO4 aqueous solutions, including in the presence of chloride ion. It has been shown that Au(III) is almost quantitatively (> 98%) extracted into the polymer-rich phase at pH ≤ 3.0 and the concentration of chloride ion >0.08 mol L−1. The developed method of gold extraction was tested on the example of electronic wastes containing Cu(II), Co(II), Ni(II), Zn(II), Fe(III), and Pb(II) ions.


#### **Table 1.**

*The examples of ABSs application for extraction of precious metals.*

*Alternative Extraction Systems for Precious Metals Recovery: Aqueous Biphasic Systems, Ionic… DOI: http://dx.doi.org/10.5772/intechopen.113354*

Simonova and coauthors studied the extraction of palladium(II) chloride complexes in an ABS (PEG-1500, PEG-115) − NaCl − (NH4)2SO4 − H2O [25]. The experimental results have shown that palladium is extracted into the organic phase by the solvation mechanism as a compound H2[PdCl4]·yPEG·nH2O. Hyphenated methods of spectrophotometric determination of palladium(II) and iridium(IV) and their separation from rhodium(III) and ruthenium(III) have been developed [31].

The effect of acid and chloride ion concentrations on phase equilibria of an ABS PEG-1500 − Na2SO4 − H2O and the partition of palladium were investigated by Milevskiy et al. [26]. The maximum distribution coefficients of palladium were achieved under extraction in ABSs PEG-1500 − Na2SO4 − 0.1 M HCl and PEG-1500 − Na2SO4 − (0.05 M H2SO4 + 0.1 M NaCl).

A method of gold extraction from scrap central processing units with an ABS based on L64 triblock copolymer, lithium sulfate, and matrix ions of the leachate solutions has been proposed [27]. Gold is quantitatively extracted in the macromolecular-rich top phase without the use of any auxiliary extractants; copper is extracted as a by-product.

Extraction of gold(III) from acidic solutions in an ABS based on PEG-6000 and imidazolium ionic liquid was carried out [28]. For this purpose, a new ionic liquid, 1-hexyl-3-methylimidazolium dodecyl sulfonate ([C6mim][C12SO3]) was synthesized. Under optimal conditions, the degree of gold extraction was 97%.

Tang et al. [29] studied the extraction behavior of palladium(II) from hydrochloric acid solution using a typical polymer-salt ABS with an ionic liquid as a functional additive. It was shown that extraction system based on PEG-2000 and K2HPO4 with imidazolium ionic liquid allowed to recover 96–99% of Pd(II) from acidic medium.

The method of extraction and separation of palladium(II) and platinum(IV) in an ABS based on PEG-1500 and ammonium sulfate from model technological solutions under dynamic conditions was developed [30]. In this case, the traditional ABS was firstly applied for extraction in a rotating coiled column (an analog of centrifugal extractor), where a polymer-rich phase is retained as a stationary phase without any solid support. A multistage extraction could be realized in the system according to the countercurrent chromatography theory [30].

#### **3. Ionic liquids**

A large number of reviews and experimental original works are devoted to ionic liquids (ILs). With ever increasing interest to fundamental and applied chemistry of ILs, the field shows no signs of slowing down. These compounds, represented as ionically bonded organic cation and organic or inorganic anion, are being defined as molten salts with melting points below 100°C. Due to their low volatility, thermal stability, and high solubility, ILs are considered to be a safer alternative to traditional molecular organic solvents [32, 33]. At the same time, compliance with the requirements for "green" solvents, namely, nontoxicity, stability, renewability, atomic efficiency, and so on, is not always feasible in the case of ILs and is determined by their composition [34, 35].

In the last two decades, studies on the use of ILs in respect to the problem of PGMs and gold separation have been actively carried out. Various ILs classified by cationic groups—ammonium, imidazolium, pyridinium, phosphonium, guanidium, and betaine—are described as exhibiting affinity and selectivity to precious metals. Examples of extraction systems based on ILs for the extraction of precious metals are quite numerous. Several comprehensive reviews on the subject have been recently published by Lee [36], Firmansyah [37], and Lanaridi [38]. The influence of the composition of cations, anions, and organic solvents on the selectivity and completeness of extraction of the target metals, as well as possible extraction mechanisms depending on the forms of metal presence in solutions, are considered in detail.

Therefore, this chapter will cover just some recent examples of the following applications of ILs:


#### **3.1 ILs as extractants**

A piperazine-based IL 1-(2-(dimethylamino) ethyl)-4-methyl-piperazin bis(trifluoromethylsulfonyl)imide ([C6-Et-TMEDA-PIP][Tf2N]2) with two functional groups was synthesized to construct an extraction system for Au(III) and Pt(IV) recovery [39]. The anion exchange mechanism was verified through the combination of methods. The stripping procedure is carried out using H2C2O4 and CS(NH2)2-HCl solutions for gold and platinum, respectively.

A commercially available quaternary ammonium salt Aliquate 336 has been used in a series of studies by Binnemans and coauthors dealing with different extraction approaches for precious metals separation [40–42]. Undiluted IL in the original chloride form [A336][Cl] or its substituted bromide form [A336][Br] enables separation of gold and palladium from base metals under nonequilibrium conditions in a milliflow set-up operating in the slug flow regime [41]. Another technique is a splitanion extraction with [A336][X] (X− = Br − and I−) developed for the separation of precious metals from aqueous chloride media. Ammonia solution, sodium thiosulfate, and thiourea were used for the selective stripping of Pd(II), Au(III), and Pt(IV), respectively, from loaded [A336][I] phase [42].

Deng et al. proposed a microemulsion extraction technique for palladium recovery from alkaline cyanide solutions using imidazolium ILs [43]. 1-butyl-3-undecyl imidazolium bromide ([BUIm]Br) was used as an extractant in a mixture of n-pentanol and n-heptane. Under optimal conditions, Pd(II) quantitatively transfers to the organic phase along with Fe(III) and Co(III) ions. The metals are separated through a two-step stripping procedure.

Quaternary ammonium chloride pseudo-protic ILs (PPILs) generated from the reaction of a primary, secondary, and tertiary amines and dissolved in toluene were used for gold(III) extraction from HCl media [44]. The metal could be conveniently precipitated as zero-valent gold nanoparticles after its stripping by sodium thiocyanate solution.

IL-based thermomorphic systems have been studied by Wang and coauthors for precious metals separation [45, 46]. UCST (upper critical solution temperature)-type *Alternative Extraction Systems for Precious Metals Recovery: Aqueous Biphasic Systems, Ionic… DOI: http://dx.doi.org/10.5772/intechopen.113354*

IL 1,4,7-trimethyltriazonane bis-(trifuloromethanesulfonyl) amide ([1,4,7-TMTA] [Tf2N]) saturated with water was used for homogenous liquid-liquid extraction of Au(III), Pd(II), and Pt(IV) at elevated temperature (40–65°C) [45]. Ethyl chloroacetate N,N,N′,N′-tetramethyl-ethylenediamine-based IL [EA-TMEDA][Tf2N]2 with temperature-responsive behavior revealed the high selectivity toward gold ions in the hydrochloric acid multicomponent solutions [46].

It should be noted that phosphonium-based ILs remain the most widely explored ILs in solvent extraction of platinum metals. Cyphos IL 101 has remarkable extraction ability to Pt(IV) and Pd(II) ions in a wide range of HCl concentrations and can be used for their recovery from various chloride-based leach solutions [47–49]. Other Cyphos ILs are full described in the above-afforded reviews [4, 5, 11, 36–38].

#### **3.2 ILs as solvents**

To separate PGMs from simulated high-level liquid waste (HLLW), a novel system containing N,N′-dimethyl-N,N′-di-(2-phenylethyl)-thiodiglycolamide (MPE-TDGA) as extractant and 1-butyl-3-methyl-imidazolium nonafluorobutansulfonate ([Bmim] [NfO]) as a solvent was proposed [50]. The system allowed the rapid and selective extraction of Pd(II), as well as Ru(III) and Rh(III). These extractions were accelerated by increasing the temperature (50°C).

#### **3.3 Synergetic mixtures of ILs**

Under carefully selected experimental conditions, the distribution coefficients of some metals in systems containing a mixture of two extractants are much higher than the additive distribution coefficient of individual extractants. This phenomenon, called synergism, is due to, as it is supposed, different types of interactions between two extractants and/or the formation of metal-containing compounds of a special composition that differs from the composition of compounds in systems with one type extractant.

A synergistic effect in the extraction of precious metals is manifested when using the mixtures of hydrophilic and hydrophobic ILs.

Chen et al. developed extraction-electrodeposition method for platinum recovery from the multicomponent solutions using the mixture of ILs [C14PIm][Br]/[C8MIm] [PF6] (1-tetradecyl-3-propylimidazolium bromide/1-octyl-3-methylimidazolium hexafluorophosphate) [51]. Pt(IV) ions were selectively separated from metal solutions containing Rh3+, Fe3+, Ni2+, Cu2+, and Zn2+ metal ions, followed by direct electrodeposition as Pt(0) on the copper cathode.

Betaine-based IL [C6Bet]Br was firstly applied to the separation of platinum metals [52]. [C6Bet]Br showed remarkable extractability for Pt(IV) and Ir(IV) in the presence of 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide [C6MIm][NTf2] as the hydrophobic phase. Ir(IV) was separated from Pt(IV) by reduction process with the use of hydroxylamine hydrochloride (NH2OH·HCl).

The synergetic mixture of the imidazolium-based ILs [C6MIm]Cl, [C6MIm] [NTf2], and [C6MIm][DDTC] (1-octyl-3-methylimidazolium chloride, bis[(trifluoromethyl)sulfonyl]imide and diethyldithiocarbamate, respectively) was offered for the extraction of Pt(IV), Pd(II), Ru(III), and Rh(III) [53]. Separation of these four PGMs can be realized by changing the composition of the synergetic mixture and concentrations of ILs.

#### **3.4 Task-specific ionic liquids (TSILs)**

These have functional group(s) involving donor atom(s) to selectively extract the targeted metal ions through metal complex formation.

A pyridinium-based TSIL with a monothioether group, 3-thiapentylpyridinium bis(trifluoromethylsulfonyl)imide [3-TPPy][NTf2], was prepared for the extraction of typical class b metal ions, including precious metal ions in high selectivity [54].

A novel extraction-photocatalysis method was developed to recover Pd from HCl leaching solutions using [C5MIm][DDTC] (1-pentyl-3-methylimidazolium diethyldithiocarbamate) as extractant [55]. The extraction was considered due to Pd-S coordination. Direct stripping of the metal can be accomplished through photocatalytic reduction process.

The TSILs bearing one or two tetrahydropyran-2H-yl(THP)-protected thiols were designed as palladium extractants from an aqueous phase to [C4MIm][NTf2] [56]. Such a kind of synergetic mixture allows to selectively bind Pd(II) ions from 4 M HCl in the presence of Pt(IV).

2-Mercaptobenzothiazole-functionalized IL ([C6mim][2MBT]) in combination with the nonionic surfactant (TX-114) was used for palladium separation *via* cloud point extraction [57]. The obtained results showed a strong coordination of palladium with anion of the IL.

An urea-based imidazolium IL, 1-butyl-3-{3-(3-methyl-2H-imidazol-1-yl)propyl} urea bis(trifluoromethylsulfonyl)imide ([C4UC3mim][Tf2N]), was synthesized and studied for Pt(IV), Pd(II) and Rh(III) separation [58]. Based on experimental data, the anion exchange mechanism was supposed for the extraction of Pt(IV) at pH = 1.13 and the inner-sphere coordination for Pd(II) extraction at pH = 5.45.

#### **3.5 ILs as a phase-forming component or as an additive in aqueous biphasic systems**

An IL-based ABSs can overcome the limitations of the use of ILs associated with their high viscosity and hydrophobicity [59]. A novel type of acidic aqueous biphasic systems (AcABS) based on an inorganic acid and an IL has been recently gaining interest for the extraction of metal ions as a promising alternative to conventional extraction systems [60]. The AcABS composed from hydrochloric acid with high concentrations and phosphonium-based IL ([P44414][Cl]) is characterized by thermotropic behavior and can be successfully applied to the separation of some strategic metals, including Pt(IV) [60].

#### **3.6 Other application of ILs**

Solid-phase extraction and membrane separation have such advantages as lower consumption of IL and its improved stability. Both technologies are considered as promising alternatives to traditional solvent extraction and deserve a separate chapter. Here are just a few references on the use of ILs as functionalizing modifiers of various solid carriers: resins, membranes, and nanoparticles [61–66].

One of the recent areas of research should also be noted. It is related to the leaching of platinum-containing materials using ILs. This approach is intended as an alternative to the refining processes, where strong acids with oxidants (aqua regia, concentrated HCl in the presence of chlorine gas or H2O2) are usually used to dissolve chemically inert platinum metals. Thus, a nonaqueous direct leaching process based on *Alternative Extraction Systems for Precious Metals Recovery: Aqueous Biphasic Systems, Ionic… DOI: http://dx.doi.org/10.5772/intechopen.113354*

trihexyl(tetradecyl)phosphonium chloride (P66614Cl) in combination with methanesulfonic acid and trichloroisocyanuric acid was proposed to solubilize metallic platinum [67].

#### **4. Deep eutectic solvents**

Since the first publication about 20 years ago by Abbott [68], deep eutectic solvents (DESs) have evolved from a subclass of ionic liquids to a wide range of liquids that have applications in many fields, including analytical chemistry and separation techniques. The original description of DES as a mixture of a salt of a quaternary ammonium base (a hydrogen bond acceptor, HBA) and a hydrogen bond donor (HBD) has been recently extended to a combination of Lewis and Bronsted acids and bases with much lower melting temperatures of the resulting mixture compared to the that of the original components [69].

DESs have a number of advantages: easy and convenient preparation, nontoxicity, non-volatility, non-combustibility, and biodegradability, which allow these compounds to be classified as environmentally benign [19, 70]. As in the case of ILs, due to the variability of constituent components, DESs are referred to designer solvents. In the emerging era of the transfer to active use of artificial intelligence, the selection of a certain composition of DESs using neural networks seems to be an extremely interesting and promising area of research [71, 72].

Publications on precious metal extraction by DESs are summarized in **Table 2**, focusing on the selected DES composition and extraction conditions. One of the pioneering works on DES application in the separation of precious metals appeared in 2019 and was devoted to the extraction of gold. Geng et al. studied the DESs based on quaternary ammonium salts for this purpose [73]. The hydrophobic DESs with [N3333]Br, [N4444]Br and [N8881]Br as HBAs and N-hexanoic acid as HBD (1:1 molar ratio) were screened out for gold recovery from hydrochloric acid solutions with various acidity and salinity. Based on combination of UV–Vis and FT-IR spectroscopy data, the anion exchange mechanism was proposed: anions [C5H13-COOH⋯Br]<sup>−</sup> are exchanged with AuCl4 − during the extraction process. The outcomes under different conditions showed that N8881Br has the best gold extraction ability and tolerance to higher salinity. NaBH4 solution (0.1 mg/L) was used as a stripping agent. The gold extraction ability of DESs was preserved during 5 cycles of extraction.

Choline chloride: phenol mixture in 1:2 molar ratio was introduced by Yilmaz et al. for gold extraction [74]. The goal of the work was to develop a sensitive method for determination of gold traces in plating bath solutions. The combined approach was used to achieve this objective: liquid phase microextraction by DES in the presence of a complexing agent and detection by flame atomic absorption spectrometry with a slotted quartz tube (SQT-FAAS). Additionally, the conventional parameters of the extraction efficiency were studied as a function of the mixing mode. Out of hand mixing, mechanical shaking, ultrasonic bath, and vortexing, the latter one was selected as the most efficient. For better phase separation, tetrahydrofuran was used for the emulsification of DES.

A similar approach and a DES of the same type were used by Panhwar et al. for palladium extraction coupled with FAAS determination in environmental samples [75]. Choline chloride:phenol mixture in 1:4 molar ratio, 2-hydroxy-3-methoxy benzaldehyde thiosemicarbazone as a complexing agent, and tetrahydrofuran as an emulsifier were dispersed in sample solution by 8 repeated cycles of quick uptaking and discharging with the use of a syringe. Selectivity of Pd(II) extraction was evaluated in the presence of Co(II), Cu(II), Cd(II), Ni(II), Mn(II), Zn(II), Pb(II), and Cr(III) ions.


#### **Table 2.**

*The examples of DES application for the extraction of precious metals.*

Four-component FeCl3-based DES was applied by ALOthman et al. for dispersive microextraction of palladium followed by FAAS determination [76]. To prepare the DES disodium 4,5-dihydroxy-1,3-benzenedisulfonate, hydroxylammonium chloride, iron(III) chloride and phenol were mixed in the ratio of 1:1:2:1. In addition to typical hydrogen-bonding interactions, the presence of FeCl3 in the formulation leads to coordination interactions with oxygen atoms of donor ligands ensuring the formation

#### *Alternative Extraction Systems for Precious Metals Recovery: Aqueous Biphasic Systems, Ionic… DOI: http://dx.doi.org/10.5772/intechopen.113354*

of a liquid. The developed procedure does not require a complexing agent; palladium recovery is quantitative and tolerant to the presence of common matrix ions.

Another kind of DES was proposed for palladium extraction by Abdi. et al. [77]. DL-menthol was mixed with phenyl salicylate (1:1), and the prepared DES was dispersed in the sample solution together with 1-(2-pyridylazo)-2-naphtol complexing agent. The extraction procedure was carried out at an elevated temperature (65°C), when the homogeneous solution was formed. The extremely low limit of detection could be achieved using the ETAAS determination method.

Abovementioned long-chain quaternary ammonium salt was investigated by Tang. et al. for the extraction of palladium from acid solutions [78]. DES was constructed by combining N8881Cl with saturated fatty acids or fatty alcohols in molar ratio 1:1 and 1:2. An anion exchange mechanism of extraction was confirmed by FTIR, UV-Vis, and 1H NMR analysis. Authors proposed stripping of palladium from the DES phase via the hydrazine hydrate reduction method; the regenerated DES was used repeatedly for Pd(II) extraction for 5 cycles.

Extraction of the whole group of platinum group metals from acid solutions with high amount of chloride-ions and matrix components was studied using DESs based on tetraoctylammonium bromide (N8888Br) and carboxylic acids [79]. The scheme of separation of Pd(II) and Pt(IV) as well as rare platinum metals was proposed for processing technological solutions to obtain individual fractions of precious metals with purity of >99.9%.

Trioctylphosphine oxide (TOPO) as HBA was mixed with various HBD reagents by Liu et al. to construct the extraction systems for Pt(IV) recovery from secondary resources [80]. TOPO-1-butanol, TOPO-L-menthol, and TOPO-1-hexanol were recommended for Pt(IV) extraction under conditions of high acidity and salinity. The ion-association mechanism of extraction was elucidated: each of the two protonated P=O groups in the TOPO molecule combined with PtCl6 2− during the process of extraction. The TOPO-1-butanol possessed the best Pt(IV) extraction ability, selectivity, and cycling extraction (using NaOH as a stripping agent).

One of the most critical and comprehensive study was carried out by Vargas, Schaeffer, and their colleagues [81, 82]. The work provides the features of Pt(IV) and Pd(II) extraction using TOPO-based DES in comparison with an equivalent extractant system in organic diluent. The conclusions of this work are quite important and deserve to be summarized here [81, 82]:


The reviewed publications demonstrate mainly the possibility of using DESs in analytical methods for the determination of three metals: gold, platinum, and palladium. The components of the studied DESs used as HBAs, namely the quaternary ammonium salts and TOPO, have been well studied in the traditional extraction of platinum metals. If the use of DESs is to be positioned as a transition to more environmentally friendly technologies, then DESs based on nontoxic compounds like choline chloride and menthol should be given a preference. However, in the case of such "green" components of the DESs, a complex-forming agent needs to be added to the extraction system [74, 75]. In order not to complicate the system and the subsequent detection stage, the design of DESs using components, which are able to complexforming or specific interaction with platinum metals for their selective recovery, is a subject of a scientific interest. The recent work, authored by Liu, has been devoted to Au(III), Pd(II), and Pt(IV) extraction using the eutectic mixture of natural components: lidocaine and thymol [83]. Thus, the search for safe and efficient eutectic extraction systems for precious metals can be expected to continue.

#### **5. Conclusion**

The imperative need to improve the existing and create new schemes for separation of PGMs and gold from complex matrices concerns both technological processes and the analytical control of the metals contents at all production stages. In many cases, selective separation of precious metals is necessary, and this is the most difficult stage of processing platinum-containing materials owing to their multicomponent composition, specific chemistry of PGMs, and their extremely low concentrations. Conventional leaching and extraction methods for the separation of precious metals involve the use of aggressive reagents and toxic solvents and are characterized by high energy consumption. The presented review confirms the relevance of fundamental and applied research in the use of alternative solvents for separation of these critical elements. At the moment, the processing of technological wastes, spent catalysts, and other secondary resources is of priority importance because of their large quantities and depletion of natural resources. In this regard, the problem of precious metals production, on the one hand, becomes a global challenge and, on the other hand, requires innovative technological solutions for countries that have primary raw materials and operate outdated approaches and materials.

Applications of ABSs, ILs, and DESs in precious metals' recycling benefit from their excellent solubility properties, extraction and electrochemical activities, and eco-friendly portfolio. Further studies in this field are likely to focus on the search for green selective components with high affinity to precious metals, especially to rare platinum metals (rhodium, iridium, and ruthenium), including the computational research and design of extraction systems, combining extraction and leaching procedures with subsequent determination, or recovery of precious metals from leachate using simple and sustainable approaches.

#### **Acknowledgements**

This work was supported by the Ministry of Science and High Education of the Russian Federation [GEOKHI RAS].

*Alternative Extraction Systems for Precious Metals Recovery: Aqueous Biphasic Systems, Ionic… DOI: http://dx.doi.org/10.5772/intechopen.113354*

#### **Author details**

Olga Mokhodoeva Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia

\*Address all correspondence to: olga.mokhodoeva@mail.ru

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 4**

## Extraction of Boron from Tourmaline Ore: Mechanism of Thermal Analysis of the Schorl

*Sneha Dandekar, Kavita Pande and Dilip Peshwe*

#### **Abstract**

Tourmaline is the chief boron-bearing mineral on the earth and is present in an excess amount in the crustal rocks. However, schorl is an iron-rich alkali that forms a solid solution with the magnesium-rich, alkali tourmaline, dravite. In this work, tourmaline (schorl variety) was treated along with soda ash, and its behavior was analyzed using electron probe microanalysis (EPMA), x-ray diffraction (XRD), scanning electron microscope, and energy dispersive spectrometer (SEM-EDS) analyses, thermogravimetric analysis (TGA), differential thermal analysis (DTA), in order to annotate the soda-ash activation of boron within the tourmaline ore. To extract boron from the sample, sodium carbonate powder was mixed with the schorl in 20% of the total weight of schorl powder. When the sample was treated with sodium carbonate, the sodium gets combined with the boron to form sodium borate at 566°C along with aegirine and aluminum oxides. This sodium borate can be treated with hydrochloric acid to get boron-oxide along with NaCl.

**Keywords:** boron, tourmaline, sodium carbonate, sodium borate, boron-oxide, extraction

#### **1. Introduction**

Tourmaline is an important and complex boron-bearing mineral on the earth and is present in an excess amount in the crustal rocks. It is not a single mineral, but a group of isomorphs minerals with identical crystal lattices. The general formula of the tourmaline group is very complex: X1Y3Al6B3Si4O27 (OH) 4 where X = Na, K, Ca and Y = Li, Fe, Mg, Mn, Al, Cr, Ti; some of the OH– ions are generally substituted by F. The boron concentration in the tourmaline has been found 3.40 ± 1% within the normal range (2.5–3.8%) reported worldwide [1]. Whereas, schorl is an iron-rich alkali tourmaline that forms a solid solution with the magnesium-rich, alkali tourmaline, dravite. It is reported that, economically sustainable deposits of borax have not been established in India so far. The only deposit of little economic importance is reported from Puga Valley in Leh district, Jammu & Kashmir. As per National Mineral Inventory data, based on the UNFC system, the

total reserves/resources of borax as of 1.4.2015, have been estimated at 74,204 tons in Jammu & Kashmir. Occurrences are also reported from Surendranagar district, Gujarat, and Jaipur district, Rajasthan [2].

Boron does not occur in free state in nature. It occurs mainly in the form of the salts of boric acid. It mainly occurs in the form of boric acid (H3BO3) and borax (Na2B4O7.10H2O). Element boron and its compounds are widely used in the industrial and agricultural sectors due to their properties such as high hardness, wear resistance, high strength, fire inhibitor, heat resistance, high strength, wear resistance, and catalytic performance. In general, boron–iron separation and dissolution activity of boron-bearing minerals in alkaline liquor are the two key issues in the utilization of tourmaline ore, governing the boron recovery as well as operating cost [3]. On a large scale, boron is extracted from its minerals, borax Na2B4O7 or colemanite Ca2B6O11. The latter is first converted to borax by boiling with a solution of sodium carbonate in the requisite proportion. In the present study, attempt has been made to extract boron by thermal analysis method.

#### **2. Materials and methodology**

Tourmaline (Schorl) was obtained from the Kyanite, Sillimanite mine of Girola area, Sakoli tehsil, Bhandara. The samples were collected, crushed, ground, and separated to 80% passing through 200 sieve size (0.074 mm). The XRD analysis of the sample was completed on Panalytical X'Pert Pro (model-PW 3040/60) diffractometer with Cu Kα radiation (λ = 1.54 Å) produced at a voltage of 45 kV and current of 40 mA. Scanning was done at the 2θ angle of 10 to 100° with a scan step size and time per step of 0.01° and 15 seconds, respectively. The surface morphology was examined using a Scanning Electron microscope (SEM-JEOL 6830A). Before the study of surface morphology, to make the material electron-conducting it was coated with a thin platinum coat using an auto sputter (JOEL-JFC 1600 auto fine coater). Whereas, the elemental composition was studied using Energy Dispersive Spectroscopy (EDS).

Electron-probe microanalysis (EPMA) of the sample was executed at the National Centre of Excellence in Geoscience Research, GSI, Bangalore using a CAMECA SX-100 electron microprobe analyzer. The spectra were collected for each sample with a wavelength-dispersive spectrometer (WDS) and with WDS 1 (TAP crystal), WDS 4 (TAP crystal), WDS 3 (LPET crystal), WDS 2 (PET crystal), and WDS 5 (LIF crystal) spectrometers. The spectra were collected using column condition of an acceleration voltage of 15 keV, beam current of 15 nA, and beam size of 1 μm. Calibration, quantification, and overlap correction were executed using CAMECA SX- 100 Peak Sight-Geo Quanta software package.

However, to extract boron from the sample, sodium carbonate powder was mixed with the schorl in 5, 10, 15, and 20% of the total weight of schorl powder. The virgin, as well as prepared samples, were roasted to 1000°C using a tubular furnace [4], and analyses were done. However, suitable boron reach compound was found to be in 20% proportion of sodium carbonate powder, hence further analysis was done of this composition by leaching out with HCl (**Figure 1**). In order to achieve the boron in pure form, acid leaching was done multiple times. However, by further synthesis iron can be removed from the compound, followed by the recovery of aluminum.

*Extraction of Boron from Tourmaline Ore: Mechanism of Thermal Analysis of the Schorl DOI: http://dx.doi.org/10.5772/intechopen.111595*

#### **Figure 1.**

*Flow chart showing the extraction process.*

#### **3. Results**

#### **3.1 EPMA**

The EPMA study was carried out for the extracted sample. From the EPMA study of the sample (**Table 1**), the mineral shows the highest content of Al2O3 of 25.88 to 61.9 wt. %, SiO2 ranges from 30.01 to 44.89 wt. %, TiO2 ranges from 0 to 1.82 wt. %, MnO content is 0 to 9.59 wt. %, MgO ranges from 0 to 14.07 wt. %, CaO ranges from


#### *Extraction Metallurgy – New Perspectives*


**Table 1.** *Showing the composition of virgin sample.*

*Extraction of Boron from Tourmaline Ore: Mechanism of Thermal Analysis of the Schorl DOI: http://dx.doi.org/10.5772/intechopen.111595*

0 to 6.92%, Na2O content is 0 to 0.95 wt. %, and K2O ranges from 0 to 0.93 wt. %. The mineral shows a high percentage of Al and considerable x-site vacancy, an intermediary between schorl, dumortierite, and dravite.

However, the EPMA analysis of the extracted sample (**Table 2**) shows the highest range of SiO2 from 41.75 to 42.8 wt. %, MgO ranges from 14.3 to 15.27 wt. %, CaO 11.15 to 11.19 wt. %, and Al2O3 9.33 to 9.49 wt. %. The content shows the presence of aegirine mineral [5].

#### **3.2 XRD**

In order to explain borate formation, an XRD analysis of the samples was done. **Figure 2** shows the XRD patterns of the untreated and treated samples. In **Figure 2a**, peak of schorl (NaFe2+ 3Al6 (Si6O18) (BO3)3(OH) 3(OH)) [6], dumortierite (Al7 BO3 (SiO4)3O3) [7] and SiO2 [8] was found. However, after the extraction (**Figure 2b**), the identified peaks correspond to sodium borate (Na2B4O7) [9], aegirine (NaFeSi2O5) [10], and Al2CO3 [11]. However, after multiple times acid leaching of the extracted sample, boron oxide was recovered (**Figure 2c**).

#### **3.3 SEM**

The surface morphology of the sample has been shown in **Figure 3**. The formation of orthorhombic-shaped dumortierite crystals [12] has been observed in SEM (**Figure 3a**). However, schorl is found in well-crystallized hexagonal-shaped along with kyanite (**Figure 3b**). The dumortierite crystals are formed after the disintegration of the tourmaline grain. However, in the extracted sample, the formation of sodium borate along with aegirine was observed. From this, it can be stated that, at a particular temperature, schorl along with sodium carbonate can form sodium borate [13] (**Figure 3c**) and aegirine ((**Figure 3d**). The acid leaching helps in the extraction of boron oxide from the mineral (**Figure 3e** and **f**), as the sodium borate reacts with HCl forming salts and boron-oxide. The Fe and Al residue gets dissolved in the solute, which can be extracted by further synthesis.

#### **3.4 TGDTA**

Three major weight losses are seen in **Figure 4a**. The first weight loss up to 85°C accounts for the dehydration of the untreated sample, which produced an endothermic peak. The second weight loss and an exothermic peak are seen at 320°C. This exothermic peak corresponded to the crystallization of FeAlO3, oxidation of Fe3+, and oxidation of Fe2+ to Fe3+. Further, an increase in temperature also triggered the decomposition of the anhydrous salt, contributing to the second weight loss. The third weight loss up to 857°C accounts for the decomposition of residual nitrate and the phase transformation of tourmaline. Therefore, the temperature of 650°C was selected as the heat-treatment temperature to protect the crystalline structure and improve the far-infrared emission of the tourmaline [14].

However, the TGDTA peak of a treated sample (**Figure 4b**). First exothermic peak at 566°C was due to the crystallization of anhydrous sodium borate (Na2 O (B2O3)2) from the amorphous phase [9, 15]. Another endothermic peak observed at 742°C was due to the melting of the crystalline anhydrous sodium borate phase.


*Extraction of Boron from Tourmaline Ore: Mechanism of Thermal Analysis of the Schorl DOI: http://dx.doi.org/10.5772/intechopen.111595*

> **Table 2.** *Showing the composition of extracted sample.*

#### **Figure 2.**

*XRD graph of (a) virgin (K- Kyanite, D-Dumortierite, S-Schorl) (b) extracted sample (A-Aegirine, T-sodium borate, C- Aluminum oxide) (c) boron recovery sample.*

*Extraction of Boron from Tourmaline Ore: Mechanism of Thermal Analysis of the Schorl DOI: http://dx.doi.org/10.5772/intechopen.111595*

#### **Figure 3.**

*SEM images of (a, b) virgin sample (c, d) extracted sample, where S- schorl, D- dumortierite, T- sodium borate, and A- aegirine, and (e, f) extracted BO3.*

#### **4. Discussion**

In order to extract boron from the tourmaline sample, it was treated with 20% of sodium carbonate power, in order to form a boron compound that will ease the element to get out of the complex tourmaline structure. On heating, the virgin, as well as extracted samples up to 1000°C following conclusions, were observed:

1.On heating the virgin sample, iron-aluminum oxides were formed at 320°C, and at the higher temperature, a transformation of tourmaline was observed. Hence, no liberation of the boron compound was found in this case.

**Figure 4.** *TGDTA graph of (a) virgin (b) extracted sample.*

2.Whereas, for the extracted sample, following reactions 1 and 2 were observed, which can state the formation of sodium borate and boron oxides, respectively.

$$\begin{aligned} &Fe^{2+} \_3Al\_6 \left(Si\_6O\_{18}\right) \left(BO\_3\right)\_3 \left(OH\right)\_3 \left(OH\right) + 2Na \left(CO\_3\right)\_3\\ &\rightarrow Na\_2B\_4O\_5 \cdot 8H\_2O + NaFeSi\_2O\_6 + AlCO\_3 \end{aligned} \tag{1}$$

$$\begin{aligned} &\bullet \, ^\text{Na}\text{B}\_2\text{O}\_5 \cdot 8\,\text{H}\_2\text{O} + \text{NaFeSi}\_2\text{O}\_6 + \text{AlClO}\_3 + 4\,\text{HCl} \\ &\rightarrow 4\,\text{B} \,(\text{OH})\_3 + 4\,\text{NaCl} + 8\,\text{H}\_2\text{O} + \text{FeCO}\_3\uparrow + \text{Al}\_2\text{O}\_3 \cdot \text{SiO}\_2 + 4\,\text{H} \end{aligned} \tag{2}$$

As, when the sample was treated with sodium carbonate, the sodium gets combined with the boron to form sodium borate at 566°C along with aegirine and aluminum carbonate (Eq. (1)). Moreover, the sodium borate when treated with hydrochloric acid forms boron-oxide along with NaCl (Eq. (2)). However, further synthesis process can be followed to remove the Fe and Al recovery from the leachate.

#### **5. Concluding remarks**

In order to extract boron from the tourmaline sample, it was treated with 20% NaCO3 and heated up to 1000°C. It was found that the sodium from the NaCO3 powder gets combined with the boron and forms sodium borate. However, the boron-oxide can be extracted by treating the sodium borate with hydrochloric acid. Extraction of boron by this method is cost-effective and can fulfill the need for boron elements in various industries.

*Extraction of Boron from Tourmaline Ore: Mechanism of Thermal Analysis of the Schorl DOI: http://dx.doi.org/10.5772/intechopen.111595*

#### **Author details**

Sneha Dandekar1 \*, Kavita Pande2 and Dilip Peshwe1

1 Department of Metallurgical and Materials Engineering, Visvesvaraya National Institute of Technology, Nagpur, India

2 Mataverse Vision Pvt. Ltd., Nagpur, India

\*Address all correspondence to: snehandandekar@gmail.com

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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